System of electrical distribution.



No. 717,298 Patented Dec. 30, I902. c. P. sTEnmETz.

SYSTEM OF ELECTRICAL DISTRIBUTION.

(Application filed Aug. 19, 1899.)

(No Model.)

\Mtnesses J nventor.

ChasP. Steinmetz. b M

T HE Nonms PETERS co. Pnnruumo.wAsumm'cm. u c

llnirrnn STATES PATENT OFFICE.

CHARLES P. STEINMETZ, OF SCHENECT-ADY, NEW YORK, ASSIGNOR TO THE GENERALELECTRIC COMPANY, A-CORP-ORATION OF NEW YORK.

SYSTEM F ELECTRICAL DISTRIBUTION.

SPECIFICATION forming part of Letters Patent No. 717,298, dated December30, 1902 Application filed August 19, 1899. erial No. 727,734. (Nomodel.)

T0 (6 whom it may concern.-

Be it known that 1, CHARLES P. STEINMETZ, a citizen of the UnitedStates, residing at Schenectady, county of Schenectady, State of NewYork, have invented certain new and useful Improvements in Systems ofElectrical Distribution, of which the following is a specification.

The invention hereinafter described emto bodies a principle of operationdisclosed in the patent to E. W. Rice, J12, No. 595,412, dated December14, 1897, fora means for regulating alternating-current dynamo-electricmachines, in which the field of a dynamo-electrio machine is regulatedby causing alternating currentfrom its armature to pass through thearmature of the exciter for said machine, thereby varying the field, andconsequently the electromotive force of the exciter, both in accordancewith the magnitude and the phase displacement of the alternatingcurrent.

To determine the scope of my invention, reference is made to the claimsin this application, in which its various features are in- 2 5 tended tobe clearly and particularly pointed out.

In its details my invention will be more readily understood by referenceto the following description, taken in connection with 0 theaccompanying drawings, in which- Figure 1 illustrates in diagram oneembodiment of my invention, while Fig. 2 is an explanatory diagram ofniagnetomotive forces.

In cases where alternatingcurrent machines of large capacity are to becompounded by passing alternating current through the armature of theexciter and in this way varying its field I find it generallyundesirable to 40 make use of the whole current for this purpose. ofthis current, derived from the secondary or secondaries of transformersthe primaries of which are placed in series with the main 5 linesleading to the machine to be regulated.

By choosing a suitable ratio of transformation it is thus possible tosupply the exciter with an alternating current which varies inproportion to the variation of current pass- 0 ing through the machineto be regulated and is at the same time of a value adapted to the Iemploy instead a fractional portion capacity of the exciter. If thedynamo-electric machine to be regulated isof the twophase type, theseries transformers thus required would ordinarily be either of thesingle-phase or two-phase type to correspond.

I have discovered that a considerable saving may be efiected by suitablymodifying the transformers in such a manner as to cause three-phasefluxes to circulate in the magnetic circuits of the transformers ratherthan two-phase fluxes, as would be the ordinary practice. A transformersuitable for effecting this result is shown in Fig. 1, in which Grepresents a two; phase generator having fieldcoils F, suitably excited,and lines or mains 1 2 3 4, leading from the collector of the machine inthe usual manner. At T is indicated a transformer-core having three legsor subdivisions. The two ouiside legs are provided with both primary andsecondary windings, while the middle leg, which forms a common returnfor the other two, may or may not be provided with winding, as will behereinafter explained. The primary windings are from necessity suppliedwith two-phase currents, and in order, therefore, to produce three-phasefluxes in the core it is necessaary to impress upon the core three-phasemagnetomotive forces, and this resultIsecure by making combinations ofmagnetomotive forces displaced in phase from each other by one-quarterof a period, but having such relative magnitudes as to produce resultantmagnetomotive forces differing in phase by one-third of a period. Themeans by which this is accomplished will be better understood byreference to the diagram shown in Fig. 2. In this figure, a I) representthe phase relation of currents flowing in the leads of the machine G,and, as 9c shown, these currents are ninety degrees or one-quarter of aperiod apart. The desired phase relation of fluxes in thetransformercore is indicated by the lines o d, which are shown asdisplaced from each other by one- 5 third of a period or one hundred andtwenty degrees. In order to produce resultant magnetomotive forcescorresponding in phase to the relation of c and d, it is necessary tocombine component magnetomotive forces 10v ninety degrees apart in sucha manner as to produce resultants one hundred and twenty degrees apart.In the proportions indicated in the diagram this has been done bycombining first the magnetomotive force a and the rnagnetomotive force6, displaced therefrom ninety degrees, thereby producing the resultantc. In a similar manner I) andf represent the relative values of twoquarter-phase magnetomotive forces required to produce a resultant d.From inspection of the figure it will be noted that the sum of theangles between co and c and between Z) and d is equal to the differencebetween the phase angles of the exciting-currents and the fluxes to beproduced thereby. So long as this relation is maintained the two anglesmay have any relative value, provided their sum remains the same. Forthe sake of uniformity, however, I have chosen to make these anglesequal to each other, in which case each will be an angle of fifteendegrees, and the magnetomotive forces, which form the components of. theresultant magnetomotive forces 0 d, will therefore be related to eachother in the ratio of the sine and cosine of fifteen degrees. In orderto cause this relation of magnetomotive forces in the transformer T, Iprovide each of the legs L L of the transformer with two primarywindings, the number of turns of the two windings on each leg beingrelated to each other in the ratio of the sine and cosine of fifteendegrees. This relation I have roughly indicated in the drawings by coilsof different sizes. In order to correspond With the diagram in Fig. 2,the windings are indicated by the letters e a bf. The windings e and I)must evidently carry current in the same phase and are thereforeconnected in series with each other and with one of the mains of thetransmission systemas, for instance, the main 1. In a similar mannerWindings a and f are connected in series with each other and with one ofthe mains of the transmission system-as, forinstance, the main 3-carryingcurrentdiffering ninety degrees from that flowing to the main 1,to which the other primary windings are connected. As thus arranged itwill be evident that when a twophase current flows in the primaryexcitingcoils three-phase fluxes are induced in the cores or legs L L Asseen, these fluxes are provided with a common return circuit formed bythe leg L of the transformer, and since two equal vectors displaced inphase by one hundred and twenty degrees form a resultant equal to eitherof its components the cross-section of the middle leg is equal to thatof either of the other legs of the transformer. The employment ofthree-phase fluxes in this manner is distinctly advantageous over theuse of two-phase fluxes, such as would ordinarily have been obtained byexciting one of the legs of the transformer from one phase only of thetransmission system and the other leg from the other phase, and thisadvantage arises from the fact that the resultant of two equal fluxesninety degrees apart in phase has a value equal to /fi times the valueof either component. With two-phase fluxes it would therefore benecessary to make the cross-section of the common return L equalapproximately to 1.42 times the cross-section of either of the legs L LThe iron loss is therefore largely reduced by the use of threephasefluxes, and a considerable amount of iron is saved. Secondary coils areplaced about two or more of the legs of the transformer, and in thesecoils three-phase electromotive forces are induced. By connecting twocoils in series-as, for instance, the coils s s and bringing connectionsfrom their free terminals and their common connection threephasecurrents may be obtained. Two sides of the three-phase triangle are thusformed by the electromotive forces acting on the system, while the thirdside remains open. If desired,however, the third electro motive forcemay be added, thereby producing a more symmetrical system. In this casea third coil 3 (shown in Fig. 1) is placed on the common return or leg Lwith its terminals connected to the outside terminals 5 6 of thesecondaries 3 .9 All three phases will thus be equally loaded.

The mode of transformation thus described is susceptible of applicationto many purposes, and I intend, therefore, to lay claim to the sameregardless of the particular use to which it may be put. In theparticular application shown, however, the three-phase lines orconductors 5 6 7, leading from the secondary of the transformer T, areconnected to collector-rings on the armature of the exciter E. Thesecollector-rings are connected to points in the armature-winding in amanner corresponding to the connection of collector-rings in athree-phase generator or 1110- tor, and therefore require no specialdescription. The eXciter E is mounted on the same shaft with thegenerator G or is otherwise mechanically driven so as to have a rate ofrotation synchronous with the generator. The simplest construction is tomake the number of poles of the generator and exciter equal and to runthem at the same speed by direct connection; but it will be obvious thatthey may be run at different speeds, provided that the relation betweenthe poles of the two machines be made to correspond. To secure thenecessary regulation of the exciter by means of the alternating currentpassed into its armature from the mains of the machine to be regulated,the angular relation of the armatures of the main machine and itsexciter is made such that the polar line produced by the alternatingcurrent is at right angles to the field of the exciter when the currentin the main machine is in phase with its induced or internalelectromotive force. Owing to the self-induction possessed by adynamo-electric machine, it may be here noted that when the current isin phase with the internal or induced electromotive force of the machineit lags with respect to the terminal voltage of the machine. Thereforewhen the machine to be regulated is working at unit-power factor thepolar line of the exciter will be advanced slightly in position, thusproducing a component of armature reaction which is arranged so as toincrease the field of the exciter, and consequently increase the fieldof the main machine, thereby compensating for the effects of self-indnotion and armature reaction.

Since the present invention is not coextensive with the broad principleof regulation above referred to, it is not necessary here to go intofurther detail. If, however, further information is desired, referencemay be had to the patent to E. WV. Rice, Jr., above mentioned.

Since the regulation of the exciter is to be secured by taking advantageof the effects of armature reaction, it is necessaryin order to securethe best results to have a comparatively weak field for the exciter inorder that it may more readily be acted upon by the reaction of thearmature-current. At the same time the armature reaction should be madeas strong as possible in order to secure the maximum effect from thecomparatively weak magnetomotive forces derived from the alternatingcurrent. When the exciter is thus constructed with a weak field andstrong armature reaction, it becomes unstable in operation and itselectromotive force varies through wide limits, with very slightvariations in speed and changes in armature reaction. To overcome thisunsteadiness of operation without destroying its characteristic mode ofaction, I construct the magnetic circuits of the field with an auxiliarypartial air-gap at some point. In the instance shown each field-pole hasa deep slit or cut K extending half-way across the pole and arranged tointercept the flux through the pole. At low magnetic densitiespractically all of the flux will flow through the iron neck,(indicated,for example, at N,) while at higher densities the neck willbecome saturated and lines of force will flow across the auxiliaryair-gap K. This introduction ofan auxiliary gap into the circuit at someselected flux density causes the saturation curve to bend, so that abovethe bend the field-flux is no longer proportional to the magnetomotiveforces producing the same, but varies at a slower rate than thevariation of such magnetomotive force. Any desired degree of stabilitymay thus be secured.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is.-

1. The method which consists in acting upon a plurality ofnon-identical, dependent, magnetic circuits by magnetomotive forcesdisplaced in phase from each other, combining the resulting fluxes toform a resultant flux and inducing an electromotive force by the actionof said resultant flux.

2. The method which consists in acting by dephased currents upon each ofa plurality of non-identical, magnetic circuits combining the resultingfluxes to form a resultant flux and inducing an electromotive force bythe action of said resultant flux.

3. The method of producing phase-differing fluxes from phase-differingcurrents of diiferent phase displacement from that of the fluxes, whichconsists in acting upon each of two dependent magnetic circuits by twomagnetomotive forces displaced in phase from each other, themagnetomotive forces acting on one magnetic circuit being related toeach other in the proportion of the sine and cosine of an angle notgreater than the difference in angle between the phase displacement ofthe fluxes and the phase displacement of the currents.

4. The method of producing three-phase fluxes from two-phase currentswhich consists in acting upon each of two non-identical magneticcircuits by two magnetomotive forces bearing a two-phase relation toeach other and related to each other in magnitude in the proportion ofthe sine and the cosine of the angle of fifteen degrees.

5. The method of producing phase-differing fluxes from phase-differingcurrents of difierent phase displacement from that of the fluxes, whichconsists in acting upon each of two magnetic circuits by twomagnetomotive forces displaced in phase from each other and related inmagnitude in the proportion of the sine and cosine of one-half thedifference in angle between the phase displacement of the fluxes and thephase displacement of the currents, and combining said fluxes to form athird flux.

6. The method of producing phase-differing fluxes from phase-difieringcurrents of different phase displacement from that of the fluxes whichconsists in acting upon each of two nonidentical, dependent magneticcircuits by two magnetomotive forces displaced in phase from each otherand related in magnitude in the proportion of the sine and cosine ofone-half the difference in angle between the phase displacement of thefluxes and the phase displacement of the currents, and combining saidfluxes to form a third flux.

7. The method of compounding a twophase dynamo-electric machine, whichconsists in producing three-phase currents proportional to the two-phasecurrents flowing in the leads of the machine, and acting by saidthreephase currents to control the field strength of said machine.

8. The method of compounding a two-phase dynamo-electric machine, whichconsists in producing three-phase fluxes varying in re sponse tovariation of current flowing in leads of said machine, causing saidfluxes to circulate in dependent magnetic circuits, generatingthree-phase current by the action of said fluxes, and utilizing saidthree-phase current to regulate said machine.

9. The method of compounding an alternating-current dynamo-electricmachine which consists in changing the number of phases of y IIO currentflowing in the leads of the machine,

flowing in leads of said machine and utilizing said three-phase currentfor regulating purposes.

13. The method of transferring energy between a quarter-phase system anda threephase system which consists in causing the transfer to take placeinductively through the medium of three-phase fluxes.

In witness whereof I have hereunto set my hand this 18th day of August,1899.

CHARLES P. STEINMETZ.

Witnesses:

BENJAMIN B. HULL, MABEL E. JAOOBSON.

